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. 2018 Aug 9;13:197. doi: 10.1186/s13018-018-0906-y

Fig. 1.

Fig. 1

Correct positioning of the calcar screws with purchase in the inferiomedial quadrant of the humeral head (left). Measurement of the head-shaft angle (HSA). The HSA is the angle created between a line perpendicular to the anatomical neck plane and the axis of the humerus shaft (right)